NOTHER NOTED climate modeler-and spokesman for
potential trouble -is James Hansen, director of
NASA's Goddard Institute (GISS) in New York City
(facing page, bottom). During the scorching hot, dry
summer of 1988 he captured international attention
when he testified before a Senate subcommittee.
"The world is getting warmer," he said bluntly. "We can
state with 99 percent confidence that current temperatures repre
sent a real global warming trend, rather than a chance fluctua
tion. We will surely have more years like this-more droughts
and many more days above a hundred degrees-in the 1990s."
He repeated these predictions in subsequent scientific meet
ings and climate symposiums-upsetting colleagues who felt he
should hedge his concerns with more qualifications and maybes.
But that is not Jim Hansen's way.
Some have heard and heeded what he and others have been
saying. Senator Albert Gore, Jr., of Tennessee, one of the most
outspoken politicians calling for action in the face of world
warming, has said bluntly: "The greenhouse effect is the most
important environmental problem we have ever faced. [It threat
ens] loss of forests, widespread drought and famine, loss of wild
species ... topsoil, stratospheric ozone .... Do we have the ca
pacity, the will, to change habits of millennia in a generation?"
Stephen H. Schneider of NCAR (right), an intense, curly
haired prophet of the future, has been deeply involved in climate
research for more than 20 years. He writes, speaks, and travels
incessantly; he is one of the worried scientists to whom policy
makers listen carefully.
"I agree with Jim Hansen and others that the world has got
ten warmer over the past century-faster than ever since about
1975," he told me. "I'm not so quick to say it's entirely due to
the greenhouse effect-though that's certainly there. Natural cli
mate variations may be at work too, reinforcing-or at other
times masking-the greenhouse forcing. In coming decades some
years and some parts of the world may be cooler, but others will
be much warmer than normal.
"The 1988 drought in North America, for example, has been
linked by colleagues at NCAR with the El Nifio phenomenon of
the tropical Pacific Ocean. A shift in the jet stream, caused by
massive ocean-atmosphere interactions in the Pacific, was the
likely cause of that hot, extremely dry summer.
"But whatever the local and temporary weather changes, the
world can't wait for proof of warming before trying to do some
thing about it. We're engaged in a huge experiment, using our
earth as the laboratory, and the experiment is irreversible. By
the time we find the greenhouse warming has damaged earth's
ability to feed its people, it will be too late to do much about it."
What would he have us do about it now? Try to slow the
release of greenhouse gases -by more rigorous energy conserva
tion and changes in fuel use (natural gas releases half as much
CO 2 as coal); by reducing the burning of rain forests, which
increases the level of CO 2 in the air; and by planting many more
trees, wherever possible.
"Keep in mind, it's not only carbon dioxide that's at fault,"
Steve Schneider points out. "Methane, which is released from
Looking ahead, climatologists
using advanced computer mod
els to predict global warming
trends have attracted wide
attention-and occasional skep
ticism. Critics say that model
ing is in its infancy and cannot
even replicate details of our cur
rent climate. Modelers agree,
and note that predictions neces
sarily fluctuate with each model
refinement.
The modelers include
Syukuro Manabe ofNOAA's
NationalGeographic, October 1990